Vehicles having an internal combustion engine have a starter. The starter may take the form of a conventional starter, a belt-driven starter-generator or a crankshaft starter-generator. The starter in each case includes an electric machine which turns a crankshaft of the internal combustion engine for starting. The electrical energy required for driving the electric machine of the starter is drawn from an electrical energy store. The energy store is normally a battery, which is also responsible for supplying an electrical system of the vehicle. The starting power or starting energy required for starting the internal combustion engine depends on a temperature of the internal combustion engine. At low temperatures, the required starting energy is greater than at higher temperatures due to a higher static friction and greater oil viscosity. Additionally, a maximally drawable discharging current decreases, particularly in a battery that is not fully charged or that has already aged. As a result, the starting reliability of conventional vehicles diminishes at low temperatures.
In order to increase the starting reliability, German Published Patent Application No. 196 01 241 describes a capacitor store connected parallel to the battery. This is charged prior to starting the internal combustion engine. A capacitor store has a lower internal resistance than a battery and is therefore able to provide large discharge currents during the starting operation nearly irrespective of temperature. A disadvantage of the device is that the capacitor store can only be charged to the voltage of the vehicle electrical system battery, which normally amounts to 14 V.
Alternatively, German Published Patent Application No. 197 52 661 describes a so-called intermediate circuit capacitor, which is connected to the vehicle electrical system via a DC/DC converter. This intermediate circuit capacitor is charged to a voltage of approximately 400 V. In the process, the low voltage limit of approximately 60 V is clearly exceeded such that costly insulating measures are required as shock hazard protection.
In both conventional devices, the vehicle electrical system supply is drawn upon to provide the starting energy such that a load is placed on the energy store of the vehicle electrical system.